Isolation and characterization of mast cells in mouse models of allergic diseases

Fetal Tissue-Derived Mast Cells (MC) as Experimental Surrogate for In Vivo Connective Tissue MC

Bone-marrow-derived mast cells are matured from bone marrow cells in medium containing 20% fetal calf serum (FCS), interleukin (IL)-3 and stem-cell factor (SCF) and are used as in vitro models to study mast cells (MC) and their role in health and disease. In vivo, however, BM-derived hematopoietic stem cells account for only a fraction of MC; the majority of MC in vivo are and remain tissue resident. In this study we established a side-by-side culture with BMMC, fetal skin MC (FSMC) or fetal liver MC (FLMC) for comparative studies to identify the best surrogates for mature connective tissue MC (CTMC). All three MC types showed comparable morphology by histology and MC phenotype by flow cytometry. Heterogeneity was detected in the transcriptome with the most differentially expressed genes in FSMC compared to BMMC being Hdc and Tpsb2. Expression of ST2 was highly expressed in BMMC and FSMC and reduced in FLMC, diminishing their secretion of type 2 cytokines. Higher granule content, stronger response to FcεRI activation and significantly higher release of histamine from FSMC compared to FLMC and BMMC indicated differences in MC development in vitro dependent on the tissue of origin. Thus, tissues of origin imprint MC precursor cells to acquire distinct phenotypes and signatures despite identical culture conditions. Fetal-derived MC resemble mature CTMC, with FSMC being the most developed.

In vitro and in vivo anti-inflammatory and anticoagulant activities of Myrciaria plinioides D. Legrand ethanol leaf extract

Myrciaria plinioides D. Legrand (Myrtaceae) is a native plant of Southern Brazil, which have potential in the food industry due to its edible fruits. Many plants belonging to this genus have been used for a variety of illnesses, including inflammatory disorders due to antioxidant properties. However, therapeutic uses of M. plinioides have been poorly studied. The aim of study was to assess the anti-inflammatory and anticoagulant activities of the ethanol leaf extract of M. plinioides. In M. plinioides extract-treated RAW 264.7 cells, assessments of cell viability, TNF-α release and p38 MAPK pathway-dependent protein expression were detected. In addition, rat paw edema models were used to analyze the anti-inflammatory effect of the extract. Macrophages cell line treated with M. plinioides extract showed a slight decrease in cell viability. In LPS-stimulated macrophages treated with different concentrations of the extract for 24 h, TNF-α release was inhibited, while modulation of p38 signaling pathway and inhibition of NF-κB p65 protein expression were dose-dependent. In rats, the extract inhibited the formation of paw edema, while an inhibitory effect on trypsin-like enzymes derived from mast cells was seen. Furthermore, the extract presented anticoagulant activity via extrinsic pathway, being able to block specifically factor Xa and thrombin. The study suggests that extract possess potent anti-inflammatory and anticoagulant effects. M. plinioides present great biological potential as a source for the development of anti-inflammatory and anticoagulant drugs. Additional studies can be proposed to better elucidate the mechanism by which M. plinioides exerts its effects.

Update on Eosinophil Interaction with Mast Cells: The Allergic Effector Unit

Mast cells and eosinophils are the key effector cells of allergy [1]. In general, allergic reactions are composed of two phases, namely an early phase and a late phase, and after that resolution occurs. If the allergic reactions fail to resolve after the late phase, allergic inflammation (AI) can evolve into a chronic phase mainly involving mast cells and eosinophils that abundantly coexist in the inflamed tissue in the late and chronic phases and cross-talk in a bidirectional manner. We defined these bidirectional interactions between MCs and Eos, as the "allergic effector unit." This cross talk is mediated by both physical cell-cell contacts through cell surface receptors such as CD48, 2B4, and respective ligands and through released mediators such as various specific granular mediators, arachidonic acid metabolites, cytokines, and chemokines [2, 3]. The allergic effector unit can be studied in vitro in a customized co-culture system using mast cells and eosinophils derived from either mouse or human sources.

MALT1 Protease Plays a Dual Role in the Allergic Response by Acting in Both Mast Cells and Endothelial Cells

The signaling protein MALT1 plays a key role in promoting NF-κB activation in Ag-stimulated lymphocytes. In this capacity, MALT1 has two functions, acting as a scaffolding protein and as a substrate-specific protease. MALT1 is also required for NF-κB-dependent induction of proinflammatory cytokines after FcεR1 stimulation in mast cells, implicating a role in allergy. Because MALT1 remains understudied in this context, we sought to investigate how MALT1 proteolytic activity contributes to the overall allergic response. We compared bone marrow-derived mast cells from MALT1 knockout (MALT1^-/-) and MALT1 protease-deficient (MALT^PD/PD) mice to wild-type cells. We found that MALT1^-/- and MALT1^PD/PD mast cells are equally impaired in cytokine production following FcεRI stimulation, indicating that MALT1 scaffolding activity is insufficient to drive the cytokine response and that MALT1 protease activity is essential. In addition to cytokine production, acute mast cell degranulation is a critical component of allergic response. Intriguingly, whereas degranulation is MALT1-independent, MALT1^PD/PD mice are protected from vascular edema induced by either passive cutaneous anaphylaxis or direct challenge with histamine, a major granule component. This suggests a role for MALT1 protease activity in endothelial cells targeted by mast cell-derived vasoactive substances. Indeed, we find that in human endothelial cells, MALT1 protease is activated following histamine treatment and is required for histamine-induced permeability. We thus propose a dual role for MALT1 protease in allergic response, mediating 1) IgE-dependent mast cell cytokine production, and 2) histamine-induced endothelial permeability. This dual role indicates that therapeutic inhibitors of MALT1 protease could work synergistically to control IgE-mediated allergic disease.

Proteoglycans involved in bidirectional communication between mast cells and hippocampal neurons

BACKGROUND

Mast cells (MCs) in the brain can respond to environmental cues and relay signals to neurons that may directly influence neuronal electrical activity, calcium signaling, and neurotransmission. MCs also express receptors for neurotransmitters and consequently can be activated by them. Here, we developed a coculture model of peritoneal MCs, incubated together with dissociated hippocampal neurons for the study of cellular mechanisms involved in the mast cell-neuron interactions.

METHODS

Calcium imaging was used to simultaneously record changes in intracellular calcium [Ca2+]i in neurons and MCs. To provide insight into the contribution of MCs on neurotransmitter release in rat hippocampal neurons, we used analysis of FM dye release, evoked by a cocktail of mediators from MCs stimulated by heat.

RESULTS

Bidirectional communication is set up between MCs and hippocampal neurons. Neuronal depolarization caused intracellular calcium [Ca2+]i oscillations in MCs that produced a quick response in neurons. Furthermore, activation of MCs with antigen or the secretagogue compound 48/80 also resulted in a neuronal [Ca2+]i response. Moreover, local application onto neurons of the MC mediator cocktail elicited Ca2+ transients and a synaptic release associated with FM dye destaining. Neuronal response was partially blocked by D-APV, a N-methyl-D-aspartate receptor (NMDAR) antagonist, and was inhibited when the cocktail was pre-digested with chondroitinase ABC, which induces enzymatic removal of proteoglycans of chondroitin sulfate (CS).

CONCLUSIONS

MC-hippocampal neuron interaction affects neuronal [Ca2+]i and exocytosis signaling through a NMDAR-dependent mechanism.

Notch ligand Delta-like1 enhances degranulation and cytokine production through a novel Notch/Dok-1/MAPKs pathway in vitro

Food allergy includes sensitization phase and effect phase, and effect cells degranulate and secrete cytokines in the effect phase, causing allergic clinical symptoms. We have demonstrated that Notch signaling plays an important role in the sensitization phase, but its role in effect phases still remains unclear. In this study, we investigated the role of Notch signaling in degranulation and cytokine production of the effect phase response. A RBL-2H3 cell model was used and Notch signaling was induced by priming with Notch ligands. Our results showed after priming with Notch ligand, Delta-like1(Dll1)-Fc, β-hexosaminidase release, and cytokines production, including TGF-β, IL-1β, IL-4, IL-6, and IL-13, were increased significantly, and the enhancement was abolished after DAPT treatment, a γ-secretase inhibitor, indicating that Dll1 Notch signaling enhanced RBL-2H3 cell degranulation and cytokine production. Western blot analysis showed that Dll1 Notch signaling augmented high-affinity IgE receptors-mediated phosphorylation of MAPKs through suppressing the expression of downstream tyrosine kinases 1 (Dok-1). Besides, a passive systemic anaphylaxis mouse model was used to confirm the role of Notch signaling. And our data showed that allergic clinical features of mice were alleviated, and the level of degranulation was decreased significantly after inhibiting Notch signaling in vivo. Therefore, we demonstrated Notch ligand Dll1 enhanced RBL-2H3 cell degranulation and cytokine production through a novel Notch/Dok-1/MAPKs pathway, suggesting Notch signaling played a key role in the effect phase of food allergy.

Immune Characterization of Bone Marrow-Derived Models of Mucosal and Connective Tissue Mast Cells

Purpose

It is well appreciated that mast cells (MCs) demonstrate tissue-specific imprinting, with different biochemical and functional properties between connective tissue MCs (CTMCs) and mucosal MCs (MMCs). Although in vitro systems have been developed to model these different subsets, there has been limited investigation into the functional characteristics of the 2 major MC subsets. Here, we report the immunologic characterization of 2 MCs subsets developed in vitro from bone marrow progenitors modeling MMCs and CTMCs.

Methods

We grew bone marrow for 4 weeks in the presence of transforming growth factor (TGF)-β, interleukin (IL)-9, IL-3, and stem cell factor (SCF) to generate MMCs, and IL-4, IL-3, and SCF to generate CTMCs.

Results

CTMCs and MMCs differed in growth rate and protease content, but their immune characteristics were remarkably similar. Both subsets responded to immunoglobulin E (IgE)-mediated activation with signaling, degranulation, and inflammatory cytokine release, although differences between subsets were noted in IL-10. CTMCs and MMCs showed a similar toll-like receptor (TLR) expression profile, dominated by expression of TLR4, TLR6, or both subsets were responsive to lipopolysaccharide (LPS), but not poly(I:C). CTMCs and MMCs express receptors for IL-33 and thymic stromal lymphopoietin (TSLP), and respond to these cytokines alone or with modified activation in response to IgE cross-linking.

Conclusions

The results of this paper show the immunologic characterization of bone marrow-derived MMCs and CTMCs, providing useful protocols for in vitro modeling of MC subsets.

Anti-allergic activity of 2,4,6-trihydroxy-3-geranylacetophenone (tHGA) via attenuation of IgE-mediated mast cell activation and inhibition of passive systemic anaphylaxis

tHGA, a geranyl acetophenone compound originally isolated from a local shrub called Melicope ptelefolia, has been previously reported to prevent ovalbumin-induced allergic airway inflammation in a murine model of allergic asthma by targeting cysteinyl leukotriene synthesis. Mast cells are immune effector cells involved in the pathogenesis of allergic diseases including asthma by releasing cysteinyl leukotrienes. The anti-asthmatic properties of tHGA could be attributed to its inhibitory effect on mast cell degranulation. As mast cell degranulation is an important event in allergic responses, this study aimed to investigate the anti-allergic effects of tHGA in cellular and animal models of IgE-mediated mast cell degranulation. For in vitro model of IgE-mediated mast cell degranulation, DNP-IgE-sensitized RBL-2H3 cells were pre-treated with tHGA before challenged with DNP-BSA to induce degranulation. For IgE-mediated passive systemic anaphylaxis, Sprague Dawley rats were sensitized by intraperitoneal injection of DNP-IgE before challenged with DNP-BSA. Both in vitro and in vivo models showed that tHGA significantly inhibited the release of preformed mediators (β-hexosaminidase and histamine) as well as de novo mediators (interleukin-4, tumour necrosis factor-α, prostaglandin D₂ and leukotriene C₄). Pre-treatment of tHGA also prevented IgE-challenged RBL-2H3 cells and peritoneal mast cells from undergoing morphological changes associated with mast cell degranulation. These findings indicate that tHGA possesses potent anti-allergic activity via attenuation of IgE-mediated mast cell degranulation and inhibition of IgE-mediated passive systemic anaphylaxis. Thus, tHGA may have the potential to be developed as a mast cell stabilizer for the treatment of allergic diseases in the future.

Transient fusion ensures granule replenishment to enable repeated release after IgE-mediated mast cell degranulation

To ensure normal immune function, mast cells employ different pathways to release mediators. Here, we report a thus far unknown capacity of mast cells to recycle and reuse secretory granules after an antigen-evoked degranulation process under physiological conditions; this phenomenon involves the existence of a recycling secretory granule pool that is available for release in a short time scale. Rapid endocytic modes contributed to the recycling of ∼60% of the total secretory granule population, which involved kiss-and-run and cavicapture mechanisms, causing retention of the intragranular matrix. We found the presence of normal-size granules and giant actomyosin- and dynamin-dependent granules, which were characterized by large quantal content. These large structures allowed the recovered mast cells to release a large amount of 5-HT, compensating for the decrease in the number of exocytosed secretory granules. This work uncovers a new physiological role of the exo-endocytosis cycle in the immunological plasticity of mast cells and reveals a new property of their biological secretion.

Identification of a New Exo-Endocytic Mechanism Triggered by Corticotropin-Releasing Hormone in Mast Cells

The key role of mast cells (MC), either in development of inflammatory pathologies or in response to environmental stress, has been widely reported in recent years. Previous studies have described the effects of corticotropin-releasing hormone (CRH), which is released from inflamed tissues by cellular stress signals, on MC degranulation, a process possibly driven by selective secretion of mediators (piecemeal degranulation). In this study, we introduce a novel granular exo-endocytic pathway induced by CRH on peritoneal MC. We found that CRH triggers substantial exocytosis, which is even stronger than that induced by Ag stimulation and is characterized by large quantal size release events. Membrane fluorescence increases during stimulation in the presence of FM1-43 dye, corroborating the strength of this exocytosis, given that discrete upward fluorescence steps are often observed and suggesting that secretory granules are preferentially released by compound exocytosis. Additionally, the presence of a depot of large tubular organelles in the cytoplasm suggests that the exocytotic process is tightly coupled to a fast compound endocytosis. This CRH-stimulated mechanism is mediated through activation of adenylate cyclase and an increase of cAMP and intracellular Ca(2+), as evidenced by the fact that the effect of CRH is mimicked by forskolin and 8-bromo-cAMP. Thus, these outcomes constitute new evidence for the critical role of MC in pathophysiological conditions within a cellular stress environment and an alternative membrane trafficking route mediated by CRH.

PGE₂ promotes apoptosis induced by cytokine deprivation through EP3 receptor and induces Bim in mouse mast cells

Increased mast cell numbers are observed at sites of allergic inflammation and restoration of normal mast cell numbers is critical to the resolution of these responses. Early studies showed that cytokines protect mast cells from apoptosis, suggesting a simple model in which diminished cytokine levels during resolution leads to cell death. The report that prostaglandins can contribute both to recruitment and to the resolution of inflammation together with the demonstration that mast cells express all four PGE₂ receptors raises the question of whether a single PGE₂ receptor mediates the ability of PGE₂ to regulate mast cell survival and apoptosis. We report here that PGE₂ through the EP3 receptor promotes cell death of mast cells initiated by cytokine withdrawal. Furthermore, the ability of PGE₂ to limit reconstitution of tissues with cultured mast cells is lost in cell lacking the EP3 receptor. Apoptosis is accompanied by higher dissipation of mitochondrial potential (ΔΨ_m), increased caspase-3 activation, chromatin condensation, and low molecular weight DNA cleavage. PGE₂ augmented cell death is dependent on an increase in intracellular calcium release, calmodulin dependent kinase II and MAPK activation. Synergy between the EP3 pathway and the intrinsic mitochondrial apoptotic pathway results in increased Bim expression and higher sensitivity of mast cells to cytokine deprivation. This supports a model in which PGE₂ can contribute to the resolution of inflammation in part by augmenting the removal of inflammatory cells in this case, mast cells.

Eosinophils interaction with mast cells: the allergic effector unit

Mast cells (MC) and eosinophils are the key effector cells of allergy (Minai-Fleminger and Levi-Schaffer, Inflamm Res 58:631-638, 2009). In general, allergic reactions have two phases, namely, an early phase and a late phase. MC and eosinophils abundantly coexist in the inflamed tissue in the late and chronic phases and cross talk in a bidirectional manner. This bidirectional interaction between MC and eosinophils is mediated by both physical cell-cell contacts through cell surface receptors such as CD48 receptors CD48, 2B4 , 2B4 and soluble mediators through various specific granular mediators, arachidonic acid metabolites, cytokines cytokines , and chemokines, collectively termed the "Allergic Effector Unit" (AEU) (Elishmereni et al., Allergy 66:376-385, 2011; Minai-Fleminger et al., Cell Tissue Res 341:405-415, 2010). These bidirectional interactions can be studied in vitro in a customized coculture system of MC and eosinophils derived from either mouse or human source.